Asphalt-surfaced roadways are built to facilitate vehicular travel. Depending upon usage density, base conditions, temperature variation, moisture levels, and/or physical age, the surfaces of the roadways eventually become misshapen and unable to support wheel loads. In order to rehabilitate the roadways for continued vehicular use, spent asphalt is removed in preparation for resurfacing.
Cold planers, sometimes also called road mills or scarifiers, are used to break up and remove layers of an asphalt roadway. A cold planer typically includes a frame propelled by tracked or wheeled drive units. The frame supports an engine, an operator's station, a milling drum, and conveyors. The milling drum, fitted with cutting tools, is rotated through a suitable interface with the engine to break up the surface of the roadway. The broken up roadway material is deposited by the milling drum onto the conveyors, which transfer the broken up material into haul trucks for removal from the worksite. As haul trucks are filled, they are replaced with empty haul trucks. The filled trucks transport the broken up material to a different location to be reused as aggregate in new asphalt or otherwise recycled. This transport process repeats until the milling process is finished.
Operators may wish to coordinate the timely arrival of empty haul trucks at the milling site with the pace of the milling process in order to improve the overall efficiency of the operation. On one hand, having too few empty trucks at the milling site can lead to increased down time when an operator must stop the cold planer to wait for an empty truck to arrive. On the other hand, too many empty trucks at the milling site can result in the wasteful under-utilization of resources. Cold planer operators typically communicate with a truck dispatcher at a material processing plant in an attempt to coordinate the movement of trucks to and from the jobsite. However, calls to the dispatcher from jobsite personnel may not always provide the dispatcher with enough information or enough time to efficiently coordinate movement of the trucks to and from the jobsite. Accurate, real-time measurement of the amount of asphalt reclaimed by the milling process of a cold planer is also desirable as a method to ensure that each individual hauling truck is not overloaded. Overloading of haul trucks may lead to violations of government regulations on maximum allowable loads for transport along public roads, as well as premature wearing of the haul trucks.
Existing cold planers typically allow an operator to adjust how quickly the rotating milling drum descends into a pavement surface to break up and remove pavement material. In some embodiments, the cold planer may be set such that the milling drum is controlled to plunge into a particular cut at a specific rate of speed, or “plunge velocity”, which may be set anywhere from a slow rate of descent to a very fast rate of descent. A touch display or other input device may be used by an operator to select the specific plunge velocity for a particular depth of cut. When a desired depth of cut is relatively shallow, such as around 2 inches, a set plunge velocity may be a relatively high plunge velocity, such as approximately 15 mm/second. Such a high plunge velocity may not cause any problems with the effectiveness of break up and removal of material because of the shallow depth of cut. However, an operator may change the desired depth of cut from a shallower depth of cut to a deeper cut such as approximately 8-10 inches, but fail to remember to also adjust the set plunge velocity accordingly. A relatively high plunge velocity for the milling drum, such as may have been appropriate for the relatively shallow depth of cut, may no longer be an appropriate plunge velocity at a deeper depth of cut for achieving an efficient and effective removal of the pavement material. Therefore, the cold planer may not work efficiently and effectively at the deeper depth of cut because the plunge velocity is too high. Moreover, the high plunge velocity attempted at a deeper depth of cut may result in excessive vibration and other wear and tear on the cutting tools and on the cold planer.
One attempt to control a cutting machine for cutting rumble strips in a road surface is disclosed in U.S. Pat. No. 8,821,063 of Johnson et al. that published on Sep. 2, 2014 (“the '063 patent”). In particular, the '063 patent discloses a system for controlling a cutting machine wherein a controller is programmed to vary a proportional gain and an error amplification signal over a range of forward speeds of the cutting machine. As an actual forward speed of the cutting machine varies between two of six predetermined input speed values a linear interpolation is applied to a last lower and next greater speed value to vary the instantaneous proportional gain and depth increment to be output by the controller.
While the system of the '063 patent may allow for automatically and continuously controlling a dimensional profile of a rumble strip cut into a road surface, no control aspects are provided for automatically setting an allowable plunge velocity or range of plunge velocities at which a milling drum may be lowered into a pavement surface to effectively and efficiently achieve a particular desired depth of cut, while minimizing wear and tear on the cutting tools and on the cold planer.
The disclosed system and method for automatically controlling a plunge velocity for a milling drum on a cold planer based on a desired depth of cut solves one or more of the problems set forth above and/or other problems in the art.